To understand speech and eventually develop communicative language skills, young children must segment and parse a complex acoustic signal. Recent theoretical accounts propose that rhythmic variations in the speech signal facilitate language acquisition by entraining neural oscillations and directing attention to specifc moments in time, such as phrase boundaries. In particular, our preliminary work shows a strong association between musical rhythm and grammar skills in typically developing children. The proposed R03 extends this work to children with Specific language impairment (SLI, a disorder which affects 7% of young children in the U.S.) to investigate rhythm deficits in this population and determine to what extent rhythm skills in these children are predictive of their language difficulties in grammar and word learning. Thus the long-term goal of this project is to identify individual differences in rhythm sensitivity that predict language acquisition outcomes, by differentiating musical and speech rhythm skills from other known factors in disordered language development, as well as illuminating the neural and cognitive mechanisms by which rhythm deficits may impede language development. This R03 proposal employs an individual differences approach as the first step towards this goal, using an original combination of methodologies drawn from child language development, cognitive neuroscience, and statistical modeling. Aims 1a and 1b of the grant will differentiate the respective contributions of speech rhythm, musical rhythm, and auditory working memory to grammar skills in children that have a wide range of grammatical abilities, in addition to investigating the role of rhythm sensitivity in SLI phenotype. Aim 2 will investigate rhythm sensitivity as a predictor in the ability of children with SLI to segment the speech signal and learn word forms. The impact of this project is a better understanding of how rhythm perception contributes to significant grammar and word learning challenges faced by children with SLI, setting the foundation for future translational research directed toward incorporating rhythm in clinical approaches to SLI. These findings are expected to lay important groundwork for future longitudinal work that will test the utility of rhythm in predicting language outcomes, including the following: response to treatments that implicitly manipulate prosody, a causal influence of rhythm training/rhythm skills on grammatical development and word learning, and utilization of rhythm sensitivity to help discern which late-talking children will resolve from those who will develop SLI.